The present invention relates to ionic compositions having a high ionic conductivity, comprising a salt wherein the anionic charge is delocalized, and their uses, such as an electrolyte.
Room temperature molten salts, such as triethyl ammonium nitrate, have been known for a long time. This product is of no interest except because of the presence of a leaving proton on the cation, limiting the redux or acido-basic stability domain of the compound. Methyl-ethylimidazolium or butyl-pyridinium type compounds, associated to the complex ion [Clxe2x88x92, xAlCl3] wherein 1 less than x less than 2, are also known. These compounds, because of the presence of the aluminium chloride, are powerful Lewis acids, hygroscopic and corrosive because they generate hydrochloric acid in the presence of humidity. Their electrochemical stability domain is also limited by the anodic oxydation of the chloride ion on one side, and by the reduction of the aluminium ion on the other side.
The use of anions usually stables associated to imidazolium or pyridinium type cations has been proposed, but the melting points are relatively high. For example, 1-methyl-3-ethylimidazolium hexafluorophosphate melts at 60xc2x0 C., and 1,2-dimenthyl-3-propylimidazolium hexafluorophosphate melts at 65xc2x0 C. In addition, these salts, although not hygroscopic, are nevertheless soluble in water and can therefore be hardly prepared by ion exchange in water unless longer alkyl substituents are used, which results in a strong reduction in conductivity and enhanced viscosity.
U.S. Pat. No. 5,827,602 describes salts with a melting point relatively low, with a selection criteria being an anion volume higher than 100 xc3x853, thus allowing to obtain salts with high conductivity and hydrophobic character. Most representative anions are the bis-trifluoromethanesulfonimidide, that has a calculated volume of 144 xc3x853 with Hyperchem(copyright) program, or the tris-trifluoromethanesulfonylmethylide, which has a volume of 206 xc3x853.
The present invention is concerned with low melting point ionic compounds, preferably lower than room temperature, wherein the cation is of the onium type and having at least one heteroatom such as N, O, S or P bearing the positive charge and is wherein the anion comprises, in whole or in part, at least one imidide ion of the type (FX1O)Nxe2x88x92(OX2F) wherein X1 and X2 are the same or different and comprise SO or PF. More specifically, the onium type cation comprises a compound of formula: 
a compound of formula 
a compound of formula 
a compound of formula 
wherein
W is O, S or N, and wherein N is optionally substituted with R1 when the valence allows it;
R1, R3, R4 are the same or different and represent
H;
an alkyl, alkenyl, oxaalkyl, oxaalkenyl, azaalkyl, azaalkenyl, thiaalkyl, thiaalkenyl, dialkylazo, each of these can be either linear, branched or cyclic and comprising from 1 to 18 carbon atoms;
cyclic or heterocyclic aliphatic radicals of from 4 to 26 carbon atoms optionally comprising at least one lateral chain comprising one or more heteroatoms;
groups comprising several aromatic or heterocyclic nuclei, condensed or not, optionally comprising one or more atoms of nitrogen, oxygen, sulfur or phosphorous; and wherein two groups R1, R3 or R4 can form a cycle or a heterocycle of from 4 to 9 carbon atoms, and wherein one or more R1, R3 or R4 groups on the same cation can be part of a polymeric chain;
R2 and R5 to R9 are the same or different and represent R1, R1Oxe2x80x94, (R1)2Nxe2x80x94, R1Sxe2x80x94, R1 being as defined above.
The invention further comprises an electrolytic composition comprising at least one ionic compound as defined above in combination with at least another component comprising a metallic salt, a polar polymer and/or an aprotic co-solvent.
It has been found that onium-type cation salts as defined above, and preferably the imidazolium, ammonium, sulfonium and phosphonium salts, associated to anions of the family represented by the general formula (FX1O)Nxe2x88x92(OX2F) as defined above allow to obtain liquid salts at temperatures equal or lower than those obtained with larger ions. Further, their conductivity is, in all instances, at the same temperature, superior to that of the compounds described in U.S. Pat. No. 5,827,602. These liquid salts are hydrophobic even though the anion size is small, comprised between 85 and 92 xc3x853, and thus, easily prepared by ion exchange in water, and can be handled without any particular precaution. Unexpectedly, these salts show an oxydation stability equal to that of the bis(trifuoromethanesulfonimidide) or tris(trifluoromethanesulfonyl)methylide anions, and higher than that obtained with anions of the tetrafluoroborate or hexafluorophoborate type.
The compounds of the present invention can, in addition to the imidide anion mentioned above, comprise at least another anion selected from Clxe2x88x92; Brxe2x88x92; Ixe2x88x92; NO3xe2x88x92; M(R10)4xe2x88x92 A(R10)6xe2x88x92; R11O2xe2x88x92, [R11ONZ1]xe2x88x92, [R11YOCZ2Z3]xe2x88x92, 4,5-dicyano-1,2,3-triazole, 3,5-bis(RF)-1,2,4-triazole, tricyanomethane, pentacyanocyclopentadiene, pentakis-(trifluoromethyl)cyclopentadiene, barbituric acid and Meldrum acid derivatives and their substitution products;
M is B, Al, Ga or Bi;
A is P, As and Sb;
R10 is a halogen;
R11 represents H, F, alkyl, alkenyl, aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl, dialkylamino, alkoxy or thioalkoxy, each having from 1 to 18 carbon atoms and being unsubstituted or substituted with one or more oxa, thia, or aza substituents, and wherein one or more hydrogen atoms are optionally replaced with halogen in a ratio of 0 to 100%, and eventually being part of polymeric chain;
Y represents C, SO, Sxe2x95x90NCN, Sxe2x95x90C(CN)2, POR11, P(NCN)R11, P(C(CN)2R11, an alkyl, alkenyl, aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl having from 1 to 18 carbon atoms and optionally substituted by one or more oxa, thia or aza; a dialkylamino group N(R10)2;
Z1 to Z3 representing independently R11, R11YO or CN, this group being optionally part of a polymeric chain.
Another advantage of the compounds of the invention is the low cost of the starting anions, their preparation not requiring perfluoroalkyl chemistry such as CF3 or C4F9 for instance, the fluorine atoms present in the compounds of the invention being derived from inorganic chemistry products, thus easily accessible. This economical aspect is particularly important because the molten salts contain between 40 and 75% by weight of the anionic species, the remainder being the cationic species. In addition, the density of these liquids is close to 1.5, compared to about 1 for the organic solutions, which requires more important quantities of salts for all applications wherein a volume or a given thickness are necessary, such as electrolyte films, chemical reactors, etc.
Another particularly important aspect of the present invention is the possibility for these molten salts to dissolve other salts, in particular metallic salts, such as lithium salts, to give highly conductive solutions. In a similar manner, the molten salts, or their mixtures with other metallic salts, are excellent solvents or plasticizers for a great number of polymers, in particular those bearing polar or ionic functions. Liquid compounds as well as polymers plasticized by ionic mixtures behaving like solid electrolytes are applicable in electrochemistry to generators of the primary or secondary type, supercapacities, electrochromic systems, antistatic coatings, or electroluminescent diodes. The non-volatility of the molten salts of the invention, their thermal and electrochemical stability, and their enhanced conductivity are important parameters for the fabrication of devices working at low temperature and not presenting the usual flammability risks associated with the use of conventional organic solvents.
The molten salts of the invention are polar media of low volatility, and because of this, are capable of being used as solvents to perform a great number of organic chemistry reactions, such as nucleophilic an electrophilic substitutions, or anionic, cationic or radicalar polymerisations. It is also possible to dissolve catalysts in such media, in particular transition metal salts or rare earth salts eventually coordinated with ligands, to increase the catalytic properties. Examples of such catalysts include bipyridines, porphyrines, phosphines, arsines. Organometallics like metallocenes are also included as solutes that can present catalytic properties.
The non-volatility of the molten salts, their thermal stability and their non-miscibility with non-polar solvents like hydrocarbons, as well as their hydrophobic character, are particularly advantageous to separate the chemical reaction products. It is also possible to work in diphasic systems, the molten salts containing the catalyst and the reacting substrates being in solution in a hydrocarbon or non-miscible aliphatic ether. After the reaction, a simple decantation can separate the organic phase containing the reaction product and the molten salt that is purified by washing with a non-solvent such as water or hydrocarbon, and dried by simple in vacuo procedure.
The ammonium, phosphonium and sulfonium cations can have an optical isomery and the molten salts containing them are chiral solvents susceptible or favoring the formation of enantiomeric excesses in the reactions performed in these media. Preferred cations for the present invention comprise the compounds of formula: 
that include the imidazolium, triazolium, thiazolium, and oxazolium derivatives;
the compounds of formula 
that include the trizolium, oxadiazolium, and thadiazolium;
the compounds of formula 
preferably pyridinium derivatives 
the compounds of formula 
wherein
W is O, S or N, and wherein N is optionally substituted with R1 when the valence allows it;
R1, R3, R4 are the same or different and represent
H;
an alkyl, alkenyl, oxaalkyl, oxaalkenyl, azaalkyl, azaalkenyl, thiaalkyl, thiaalkenyl, dialkylazo, each of these can be either linear branched or cyclic and comprising from I to 18 carbon atoms;
cyclic or heterocyclic aliphatic radicals of from 4 to 26 carbon atoms optionally comprising at least one lateral chain comprising one or more heteroatoms such as nitrogen, oxygen or sulfur;
aryl, arylalkyl, alkylaryl and alkenyaryl of from 5 to 26 carbon atoms optionally comprising one or more heteroatoms in the aromatic nucleus;
groups comprising several aromatic or heterocyclic nuclei, condensed or not, optionally comprising one or more atoms of nitrogen, oxygen, sulfur or phosphorous; and wherein two groups R1, R3 or R4 can form a cycle or a heterocycle from 4 to 9 carbon atoms, and wherein one or more R1, R3 or R4 groups on the same cation can be part of a polymeric chain;
R2 and R5 to R9 are the same or different and represent R1, R1Oxe2x80x94, (R1)2Nxe2x80x94, R1Sxe2x80x94, R1 being as defined above.
R1, R3 and R4 groups can bear groups active in polymerization such as double bonds or epoxides, or reactive functions in polycondensations, such as OH, NH2 or COOH. When the cations bear double bonds, they can be homopolymerized or copolymerized, for instance with vinylidene fluoride, an acrylate, a maleimide, acrylonitrile, a vinylether, a styrene, etc. Epoxide groups can be polycondensed or copolymerized with other epoxides. These polycations are particularly useful alone or in a mixture with a solvent, including a molten salt of the present invention and/or one or more lithium salt or a mixture of lithium and potassium salts as electrolyte in lithium batteries with a lithium anode or using a cathode inserting the lithium at low potential such as titanium spinel or carbonated materials.
The invention further concerns an electrolytic composition comprising at least one ionic compound comprising at least one anion and at least one cation as defined above in combination with at least another compound comprising a metallic salt, a polar polymer and/or an aprotic co-solvent. A preferred cation of the metallic salt comprises the proton, an alkaline metal cation, an alkaline-earth metal cation, a transition metal cation, a rare earth metal cation, lithium being particularly preferred.
A preferred polar polymer comprises monomer units derived from ethylene oxide, propylene oxide, epichlorohydrine, epifluorohydrine, trifluoroepoxypropane, acrylonitrile, methacrylonitrile, esters and amides of acrylic and methacrylic acid, vinylidene fluoride, N-methylpyrrolidone and polyelectrolytes of the polycation or polyanion. Finally, examples of preferred aprotic co-solvent include di-alkylic ethers of ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycols of weight comprised between 400 and 2000; esters, in particular those of carbonic acid, linear or cyclics such as dimethylcarbonate, methyl-ethylcarbonate, diethylcarbonate, ethylene carbonate, propylene carbonate; esters like y-butyrolactone, nitrites like glutaronitrile, 1,2,6-tricyanohexane, amides such as dimethylformamide, N-methylpyrrolidinone, sulfamides and sulfonamides as well as mixtures thereof.
When the present electrolytic composition comprises more than one polymer, is at least one of those can be cross-linked.
An electrochemical generator comprising an electrolytic composition of the present invention preferably comprises; a negative electrode containing either lithium metal or an alloy thereof, or a carbon insertion compound, in particular petroleum coke or graphite, or a low potential insertion oxide such as titanium spinel Li4xe2x88x92x+3yTi5xe2x88x92xO12 (0xe2x89xa6x, yxe2x89xa61), or a double nitride of a transition metal and lithium such as Li3xe2x88x92xCozN (0xe2x89xa6zxe2x89xa61) or having a structure of the antifluorite type like Li3FeN2 or Li7MnN4, or mixtures thereof. The positive electrode of the generator preferably contains either vanadium oxide VOx (2xe2x89xa6xxe2x89xa62,5), a mixed oxide of lithium and vanadium LiV3O8, a double oxide of cobalt and lithium optionally partially substituted of general formula Li1xe2x88x92xcex1Co1xe2x88x92x+yNixAly(0xe2x89xa6x+yxe2x89xa61; 0xe2x89xa6yxe2x89xa60,3; 0xe2x89xa6xcex1xe2x89xa61), a manganese spinel optionally partially substituted of general formula Li1xe2x88x92xcex1Mn2xe2x88x92zMz (0xe2x89xa6zxe2x89xa61) wherein M=Li, Mg, Al, Cr, Ni, Co, Cu, Ni, Fe; a double phosphate of the olivine or Nasicon structure such as Li1xe2x88x92xcex1Fe1xe2x88x92xMnxPO4, Li1xe2x88x92x+2xcex1Fe2P1xe2x88x92xSixO4 (0xe2x89xa6x, xcex1xe2x89xa61), a rhodizonic acid salt, a polydisulfide derived from the oxidation of dimercaptoethane, 2,5-dimercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-oxadiazole, 1,2-dimercaptocyclobutene-3,4-dione, or mixtures thereof.
Advantageously, at least one of the electrodes of the generator is mixed with the electrolytic composition to form a composite electrode.
The electrolytic composition of the invention can also be used as an electrolyte in an electrical energy storage system of the supercapacity type, optionally containing, in an electrode, carbon with high specific surface, or a conjugated polymer. Advantageously, the conjugated polymer comprises 3 degrees of oxidation, and is found in both electrodes. An example of such a polymer is a derivative of phenyl-3-thiophene.
Finally, the electrolytic composition of the invention can be used as an electrolyte in a light modulating system of the electrochromic type comprising as least one electrochromic material. In such a system, the electrochromic material is advantageously deposited on a layer of a semi-conductor transparent in the visible, preferably a tin oxide or indium oxide derivative, on a glass or polymer substrate. Examples of preferred electrochomic materials include oxides of molybdenum, tungsten, titanium, vanadium, niobium, cerium, tin, and mixtures thereof The electrochromic material can optionally be dissolved in the electrolyte.